The three experiments described in this paper were intended to show whether voluntary attention to a particular part of the peripheral visual field had any effect on the accuracy of the subject's perception. Test objects near to threshold value (for acuity or for changes in luminance) were used. The experiments were also designed to study the possible distracting effect of other stimuli presented simultaneously in different parts of the field. In Experiment 1 the subject could be given foreknowledge of the position in which an acuity test object would appear. In Experiment 2 the signal of where to attend was given simultaneously with the exposure of an acuity test object. In Experiment 3 differential thresholds for luminance were investigated by methods similar to those used in Experiment 2. It was found in all these cases that the instructions to attend to a particular part of the peripheral field had no significant effect on perception unless there were simultaneously exposed “competing” stimuli in other parts of the field. The results support the view that, in peripheral vision, attention acts selectively on the immediate memory trace only when there is a complex pattern of stimulation.

1. Introd&y (p. 173). 2. Exp. 1: Food-tray in sight (pp. 173-175). 3. Exp. 2: Food-tray out of sight (pp. 176-177). 4. EXP. 3: ~e a r n i~~~ with TW reward (pp. 178-180). 5. Conclusions (p. 180). 1. INTRODUCTORY.IN many experiments on learning in animals the food-seeking tendency is used as an incentive, and it has been shown(1) that in these cases the rate at which an animal learns is dependent on its state of hunger. It might be expected that the rate of learning would also be dependent on the amount of food given as .a reward for successful performance,. but this problem, although it is of considerable theoretical importance, does not seem to have been investigated. Yerkes and Dodson(2) have, however, described some very interesting experiments on the influence of the amount of punishment given for unsuccessful performance on the rate of learning in mice, and Cole(3) has studied the same problem in chickens; while Hoge and Stocking@) and Dodson(1) have compared the effectiveness of certain rewards with that of certain punishments, and Stone and Sturman-Humble (5) have compared the value aa incentives of food-seeking and sex.The present paper describes briefly some experiments on the influence of the amount of food given as a reward on the rate at which young chickens learn certain relatively simple performances. EXP. 1: FOOD-TRAY IN SIUHT.The apparatus in this experiment consisted of a passage 4ft. long and 8 in. wide at one end of which was a release-box. I n the preliminary training the chicks were trained individually to run out of the release- 12-2

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Movement in a part of either of two binocular fields can, under some conditions, produce temporary obliteration of the corresponding part of the other field. This paper is a mainly qualitative study of this rather surprising phenomenon. The effect is found to increase from the fovea to the periphery, to be greatest at a velocity of about 20° visual angle per sec. and to vary with the orientation of the fixation point in the visual field. Some further lines of research designed to elucidate the relation of the effect described here to certain other visual phenomena are suggested.

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